The present disclosure relates to a slot-die coating method and apparatus for manufacturing a patterned coating layer on a substrate. The disclosure further relates to a substrate manufactured by such a method.
Organic coatings layers are typically applied to a substrate as a liquid solution, e.g. for manufacturing OLED or OPV devices. For many applications, e.g. manufacturing of photo-active layers and/or light-emitting layers, it may be desired to provide one or more homogeneous coating layers on a substrate, i.e. having a homogeneous layer thickness. One technique for manufacturing a homogeneous coating layer may be referred to as “slot-die coating”. This technique typically comprises providing a slot-die coating head arranged over a substrate surface. The slot-die coating head comprising an outflow opening forming a slit that is arranged in a slit direction over the substrate surface. A coating fluid, e.g. supplied by a coating fluid supply, flows through the outflow opening onto the substrate surface. A relative movement between the outflow opening and the substrate surface is controlled along a coating direction. The coating direction is typically transverse, i.e. having a perpendicular component, to the slit direction. In this way a homogeneous layer may be manufactured along a width of the slit onto the substrate surface.
In addition to having a homogeneous coating layer, it may be desired to provide a patterning of the coating on the substrate surface, e.g. wherein the patterned coating comprises coated areas on the substrate surface separated by uncoated areas. For example, for the manufacture of photo-active layers and/or light-emitting layers it may be desired to provide separated active areas on a substrate, e.g. for building an array of photo-cells. Many different methods are known for providing a patterned coating layer, e.g. printing or imprinting techniques such as inkjet printing, rotatory screen printing, gravure printing, offset printing, flexo printing. Unfortunately, in practice these processes do not always provide a desired homogeneity of the coating layer and/or suitability for large scale production, e.g. in a roll-to-roll process. It may thus be advantageous to use a patterning technique that can be combined with a slot-die coating process.
A first option for manufacturing a patterned coating with slot-die coating may be referred to as “in-situ patterning” or “active patterning”, wherein the slot-die coating head is actively used for selectively applying the coating on specific areas of the substrate. In one example, an intermittent transfer is controlled of the coating fluid from the slot-die coating head onto the substrate surface, e.g. by switching a valve between the slot-die coating head and the coating fluid supply and/or selectively removing the slot-die coating head from the substrate. In this way coated areas may be provided having boundaries transverse to the coating direction. Unfortunately, it is found that an intermittent switching of the supply and/or removal and reapplication of the coating head may result in edge effects wherein the coating is no longer uniform e.g. due to the accumulation of coating material on the coating head.
For example, U.S. Pat. Nos. 7,041,336 and 5,536,313 describe problems with edge effects and propose adaptations to the nozzle to better control the flow-rate out of the nozzle when the flow is interrupted. U.S. Pat. No. 6,475,282 proposes to overcome the problem of leading edge anomalies by monitoring the amount of extrusion material directed to the surface and away from the surface to enable precise control of flow conditions. Disadvantageously, these solutions may lead to a complicated nozzle design. Furthermore adaptation of the flow-rate may not solve specific edge effects, e.g. caused by excess coating fluid sticking to the tip of the coating head and/or caused by lift-off and landing of the coating head on the substrate.
In stead of active patterning, a second option for manufacturing a patterned coating in a slot-die coating process may be referred to as “pre-patterning”, wherein a surface energy of the substrate is locally altered by pre-treatment according to a specific pattern. Advantageously, the coating fluid may be applied to the substrate in the same way as for non-patterned slot-die coating, i.e. the slot-die coating head does not require any adaptations, e.g. complicated nozzle designs or a means to displace the coating head. Instead, due to the pre-patterning on the substrate, the coating fluid may automatically dewet areas having relatively low surface energy, e.g. hydrophobic or lyophobic parts, and travel to nearby areas having relatively high surface energy, e.g. hydrophilic or lyophilic parts. In this way a desired pattern may be created by self-assembly. For example, US2008/0075837 describes creating lyophobic or lyophilic surface patterns on a flexible substrate in a roll-to-roll process. Unfortunately, also pre-patterning techniques may suffer from “edge effects” wherein the coating is no longer uniform, e.g. caused by the coating accumulating from the low energy areas to the edges of the high energy areas.
Alternatively still, a third option for manufacturing a patterned coating in a slot-die coating process may be referred to as “post-patterning”, wherein a homogeneously applied coating may be selectively removed after deposition. For example, selected parts of the coating layer may be removed by means of wiping, re-dissolving or laser ablation thereby forming a desired pattern. However, wiping and re-dissolving may also suffer from edge effects wherein the coating is no longer uniform. In addition, while laser ablation may be suitable for avoiding some of these effects this technique may not be economically viable for large scale production e.g. due to speed limitations.
There is yet a desire for a comprehensive and economically viable method and apparatus for manufacturing a patterned coating with coated areas having improved homogeneity of the coating layer thickness.